This invention relates to electrical storage heaters of the kind (hereinafter referred to as being of the kind specified) comprising a heat store, electrical heating means for heating same, a circuit (herein called the charging circuit) including charge control means for regulating the flow of current to the electrical heating means during an off-peak charging period, means providing for flow of air or other heat distributing fluid (herein for convenience referred to as air) into contact with the heat store and thereafter to a space or place to be heated, and flow control means for controlling the flow of said air.
The electrical heating means is ordinarily powered from an electrical supply source (herein called the off-peak supply) which is operative, i.e. rendered live, by timed controlled switch means not accessible to the user for one or more restricted periods (herein called off-peak periods) during each basic twenty four hour period. One of such off-peak periods which is frequently utilised extends from 2400 hours to 0700 hours and in some cases a second off-peak period is provided extending from 1300 hours to 1500 hours.
In our European Patent Application 80301045.3 we have disclosed and claimed an electrical storage heater of the kind specified in which the flow control means is adjusted to regulate flow of air as a function of both the temperature of the heat store and the temperature of air entering the heater from the space or place to be heated.
The control aspect with respect to the temperature of the heat store, although adequate to ensure that external parts of the heater casing which the use may touch, such as the heater output grille, are never dangerously hot, is unable to offer an identical heat output characteristic independently of the amount of heat stored at the beginning of each day (on-peak) period. Such adjustment as is necessary must be effected by the use of a manually adjustable control member. For example, a unit which is manually adjusted for cold weather operation (maximum stored heat) may have the flow control means gradually opening towards the latter part of the day, say evening, in order to boost the heat output when the naturally-cooling casing of the heater is emitting less heat than earlier. On a subsequent (warmer) day, when the off-peak heat storage is less, and the heater starts the day with less heat stored and is of lower general temperature at the casing, the flow control means, left without alteration to its manual adjuster knob, will operate on a different characteristic and will undesirably boost the heat output earlier, leaving the evening period without sufficient heat.
In our British Patent GB 2097912B we have disclosed and claimed on electrical storage heater of the kind specified in which the charge control means is responsive to the temperature of air in the space or place to be heated (and hence indirectly to weather temperature). One of the problems encountered is that although control of the flow control means as a function of store temperature and temperature of the air in the space or place to be heated (during an on-peak period) provides a satisfactory degree of sophistication in terms of attaining the level of heating desired by the user while maintaining optimum or near optimum economy, performance can be upset by changes in weather temperature occurring between the terminal portion of the preceding off-peak period (when the level of charge is determined at least in part by weather temperature) and the on-peak period in question.
However there do occur variations in the heating parameters which desirably are accommodated for in the control of the output from the heater, for example when, due to a mild night, the level to which the heater is charged during the off-peak period is reduced.
Where the temperature of the room is to remain at a relatively high level, no problem would be encountered, since the sensed reduction in the temperature of the heat store would be opposed by the sensed increase in the temperature of the room being served. However, should the room temperature return to its original temperature, the combined effect of the temperature sensing elements would cause a response similar to a reduction in room temperature, and in consequence would produce an increase in the temperature of the room being served, causing an unduly high rate of heat dissipation.